A ball grid array (BGA) is generally known as a semiconductor package structure that is mounted on a printed circuit board with high density. The BGA allows a semiconductor package to be mounted on a printed circuit board by joining solder balls provided for the semiconductor package to the printed circuit board.
In some cases, a recent increase in size of semiconductor packages and printed circuit boards causes curving (warping) of a printed circuit board when a semiconductor package is mounted on the printed circuit board. If the printed circuit board is caused to curve, a load is applied to a BGA joining portion, so that a crack (hereinafter, referred to as “solder crack”) may occur in a solder ball.
According to a method of detecting the occurrence of such a solder crack, a semiconductor package including solder balls connected in a daisy chain pattern and an evaluation board in which a daisy chain pattern corresponding to the above daisy chain pattern is formed are prepared, the semiconductor package is mounted on the evaluation board, and the resistance (hereinafter, “connection resistance”) of connection between the solder balls and pattern segments are measured. If a solder crack occurs in at least one portion, the connection resistance increases. The increase in connection resistance is detected, so that the occurrence of an abnormality is determined.
Another method of detecting a solder crack uses a strain gauge that is placed in a position near a corner of a semiconductor package mounted on a printed circuit board. According to this method, mechanical stress (strain) which occurs in a surface of a substrate of a printed circuit board is measured using the strain gauge. Instead of a resistance, fracture life (allowable strain) leading to a solder crack is estimated on the basis of the result of measurement.
As for the method using the daisy chain pattern, however, which solder ball has an abnormality, namely, a position where the abnormality has occurred may not be specified because all of the solder balls are connected in the daisy chain pattern. In order to specify the position where the abnormality has occurred, it is therefore necessary to perform destructive inspection on, for example, the cross section. Disadvantageously, it takes time to specify the position where the abnormality has occurred.
In addition, since the daisy chain pattern is an evaluation pattern in which all of the solder balls are connected (short-circuited), it is impossible to set the daisy chain pattern on a printed circuit board to be an actual product. Disadvantageously, an abnormality of a solder ball may not be detected in a product which will be actually shipped by the method using the daisy chain pattern.
According to the other method using a strain gauge which is placed on a printed circuit board, strain is detected only in a measurement position that is apart from positions where solder balls are actually joined. Disadvantageously, the accuracy of estimation of fracture life is reduced.
Japanese Laid-open Patent Publication No. 2005-268706 is example of related art.